The present invention relates generally to fuel cells, and, more particularly, to air breathing direct methanol fuel cells.
As portable consumer electronics become increasingly popular, there is a strong demand for long lasting portable power sources in the range of a few hundred milliwatts to a few wafts range. At present, these demands are largely met by various types of batteries. Often, these batteries are very expensive, short-lived and all have disposal problems.
Methanol fuel cells are a promising technology for these types of battery replacement applications. Methanol, as the fuel, has a high energy density and is easily obtained, stored and transported. Direct methanol fuel cells and stacks with forced airflow on the cathode side and forced methanol flow on the anode side have been under development at Los Alamos National Laboratory for the past 5 years, both for portable power and for transportation applications. Usually, this type of direct methanol fuel cell works at elevated temperature, requiring various auxiliary components and a rather complicated control system. Such a direct methanol fuel cell does not fit the requirements for the low power battery replacement applications.
For such applications using a direct methanol fuel cell, the key challenges are to provide acceptable power output, high energy conversion efficiency, and high energy density with the cell operated in convenient conditions to the user. The typical desired operating condition are, for example, an operating temperature near room temperature, no forced air flow, no re-circulation methanol pump, and no water recovery system. In the present invention, a direct methanol fuel cell is passive, i.e., operates under no forced air (i.e., air breathing) at near room temperature. This type of cell is referred to herein as an air breathing direct methanol fuel cell (air breathing DMFC).
Various aspects of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention includes an air breathing direct methanol fuel cell having a membrane electrode assembly, a conductive cathode assembly permeable to air and directly open to atmospheric air, and a conductive anode assembly permeable to methanol and directly contacting a mixture of liquid methanol and water. Water loss from the cell is minimized by making the conductive cathode assembly hydrophobic and the conductive anode assembly hydrophilic.